This invention relates to a self-propelled vibratory plate excited by unbalance vibrations and comprising an unbalance vibrator of the type having casing, a rotating unbalanced rotor mounted in said casing for generating a rotating eciting centrifugal force, said casing being located on the front portion of a ground plate, said unbalance vibrator being in drive connection with an engine, which is supported on said ground plate through resilient elements.
Such a vibratory plate, having an unbalance vibrator for generating rotating forces located near its forward end, moves in a forward direction when the vibrator is in operation. Due to the centrifugal force of the vibrator, the plate is alternatingly pressed down to the ground or lifted from the ground. Immediately following the "pressing-down phase" the ground plate remains in contact with the ground. This results in the then acting rearward component of the centrifugal force failing to produce any corresponding movement of the vibratory plate. Subsequently, the plate is lifted from the ground by the upward-acting centrifugal force. During this subsequent "flight phase", one component of the centrifugal force is forward-acting, whereby the vibratory plate is moved a short distance forward, until it is again pressed down to the ground by the then downward-acting centrifugal force. With this type of machine, the compacting effect is achieved by the alternating forces exerted by the unbalance vibrator. It is necessary, on one hand, to achieve a sufficient forward movement and, on the other hand, not to consume the major portion of the centrifugal force exerted by the unbalance vibrator by accelerating the mass of the ground. Therefore, the ground plate has to be as lightweight as possible but has, nevertheless, to provide sufficient rigidity.
A lightweight ground plate can be achieved by the use of thin material, for example, by the use of welded structures from the steel plate. Using a thin material, however, necessitates optimum structural design in order, on one hand, to provide the required rigidity of the whole structure and, on the other hand, to make sure that the saving in weight achieved by small thickness of the material is not compensated by an increase in weight due to the required additional reinforcements.
It is an object of the invention to provide a self-propelling vibratory plate of the type defined in the beginning in which sufficient rigidity is achieved with low weight of the plate, resulting in good compacting power and high traveling speed of the vibratory plate.
In accordance with the invention, said casing of the unbalance vibrator is integral with said ground plate and is, on one hand, integral with the upwardly extending front edge of the ground plate substantially along the total width thereof and, on the other hand, is supported on the ground plate through ribs which are located in the bearing planes of the rotor shaft.
Thus, there is a reinforcement of the ground plate in the area exposed to particular load, this reinforcement being effected by the vibrator casing integral with the ground plate, and the ribs, which together form a rigid structure. Through the ribs, the downward-acting component of the centrifugal force is transmitted without bending moments to the ground plate.
Use of a welded structure will result in a rather high proportion of welding work. For this reason, it is advantageous if the ground plate, the vibrator casing and said ribs are one integral cast body. Furthermore, the space limitations may be such as to make welding impractical due to lack of accessibility to the joints to be welded.
The self-propelling characteristics of the vibratory plate can be improved by having the underside of the front end of the ground plate in the form of a double bevel. The forward-most bevel, which is the steeper of the two, permits the ground plate to climb even on rather high projecting ground portions, while the adjacent less steep bevel permits such ground portions to be compressed by the vertical component of the centrifugal force at a more favorable angle.
From the front edge of this double bevel, the structure may extend upwardly and rearwardly, the portion at said forward edge being connected to the vibrator casing. This results in a substantially closed cover along the front of the ground plate and a favorable rigid structure comprising the double beveled portion, the front edge portion and the ribs.
The front edge portion may have an aperture therethrough in the space between the ribs. This aperture enables the machine to be engaged in order to lift the front portion of the machine or to pull the machine away from an obstacle, etc. In addition, the aperture is advantageous from the point of view of making the casting. The ground plate may be slightly beveled at its rear. In addition, the ground plate may have reinforcements along its side edges. To provide a further reinforcement there may be a transverse reinforcing rib on the upper surface of the ground plate, said reinforcing rib being integral, on one hand, with the ground plate and, on the other hand, with the rear edges of said ribs in the bearing planes of the rotor shaft. Also, this results in increased rigidity of the structure. The transverse reinforcing rib may have a central aperture substantially in alignment with the aperture of the forward edge portion. Thus, for example, a hauling rope may extend through the two apertures and below the vibrator casing.
The engine may be mounted on an engine plate, which is resiliently supported at its front and rear ends on the ground plate through cylindrical rubber elements, at least the front rubber elements having their axes substantially in longitudinal direction of the ground plate. Thus the resiliency of the rubber elements keeps a belt between the engine and the unbalance vibrator permanently tensioned so that the tension does not relax by vibrations of the engines, particularly in the resonance range. Such a relaxing of the tension could result in a decrease of the transmitted power. By maintaining the tension, it becomes possible to use an engine of reduced peak power output. Advantageously the front rubber elements are supported on the ground plate through said reinforcing rib.
A particularly lightweight construction is achieved in that said ground plate is cast from aluminum and has a steel facing on its bottom surface. Alternatively, the ground plate may be made of fiberglass reinforced plastic with a steel facing on its bottom surface. In both cases the steel facing may be adhesively secured to the bottom surface of the main body of the ground plate.